1. Field of the Invention
The present invention relates to a control method of an AC motor for preventing torque reduction and torque ripple, and an unstable phenomenon in a voltage source inverter of a PWM system.
2. Description of the Related Art
In a voltage source inverter of a PWM system, a P side switching device and an N side switching device constituting the inverter are alternately rendered conductive to control an output voltage. However, since due to the turn-off time a delay occurs in the switching of the switching devices, only one of the switching devices is turned on when a predetermined period (a dead time) has elapsed following the switching off of the other switching device, and the P side and the N side switching devices are not turned on at the same time.
In the related voltage source inverter of the PWM system, especially in a case wherein the output frequency of the inverter is low, simply because the output voltage is low, extensive fluctuation and distortion of the output voltage occurs because of the dispersion of the dead time. Thus, as problems, the torque of a motor controlled by the inverter is reduced, and torque ripple and an unstable motor phenomenon occur.
A known conventional adjustment method is the one described in patent document 1, whereby a shift in a dead time (an on-delay) compensation value is automatically adjusted.
Patent Document 1: International Patent Publication WO98/42067(PCT/JP97/00909)